fix(loops): lock the count+insert and the list read

[byrongamatos]

Follow-up to #839. Fixes two pre-existing races CodeRabbit flagged on the loops routes there — the verbatim extraction moved them unchanged from server.py, so they correctly weren't fixed in the move-only PR (both are byte-identical to 6c98aba:server.py).

1. save_loop auto-naming was not atomic. COUNT(*) ran outside meta_db._lock, then the INSERT ran inside it. Two simultaneous unnamed POSTs read the same count and both mint Loop N. → COUNT + INSERT now share one lock scope.
2. list_loops read the shared connection unlocked. The single check_same_thread=False connection is serialized through _lock by every writer, so an unlocked SELECT can overlap a POST/DELETE commit. → read under the lock.

Low severity in context — FeedBack is single-user (Principle I), so concurrent unnamed-loop POSTs essentially can't happen — but each fix is one lock scope, so it's worth doing.

Test

tests/test_loops_concurrency.py releases 16 workers into save_loop at once via a threading.Barrier and asserts no two auto-named loops collide. Negative-checked: reverting the COUNT back outside the lock fails the uniqueness assertion 5/5 runs; the fix passes 3/3. A second test hammers list_loops against 40 concurrent writes and asserts no error.

pytest 2400 passed; on-device, two unnamed POSTs → ['Loop 1', 'Loop 2']. Codex 0 findings.

Closes the two review threads on #839.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Improved reliability when saving loops concurrently.
  • Prevented duplicate automatically generated loop names.
  • Improved stability when viewing loops while saves are in progress.

• Tests

  • Added coverage for concurrent loop creation and simultaneous reading and saving.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fd101d04-2c50-466c-b4b8-647aedae3e14

📥 Commits

Reviewing files that changed from the base of the PR and between b41361e and ea6a797.

📒 Files selected for processing (2)

• lib/routers/loops.py
• tests/test_loops_concurrency.py

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📝 Walkthrough

Walkthrough

Loop database reads and writes now use the metadata database lock. Auto-generated names are counted and inserted within one locked transaction, with concurrency tests covering simultaneous saves and interleaved reads and writes.

Changes

Loop concurrency handling

Layer / File(s)	Summary
Serialize loop database operations lib/routers/loops.py	list_loops locks SQLite reads, while save_loop keeps auto-name generation, insertion, and commit within the same lock scope.
Validate concurrent loop access tests/test_loops_concurrency.py	Tests verify unique generated names, expected insert counts, and error-free concurrent reads and writes.

Estimated code review effort: 3 (Moderate) | ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main concurrency fix in loops: locking the count+insert path and list reads.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/loops-lock-atomicity

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